The overall objective of this investigation is to study the mechanism of action of the antitumor agents adriamycin, its analogs 4'-epi-adriamycin, 4-demethoxyadriamycin, the beta-anomer of adriamycn, N-trifluoroacetyladriamycin-14-valerate (AD32) and N-trifluoroacetyladriamycin (AD41). During the current year we have been investigating the effects of adriamycin, AD32, ad 4'-epi adriamycin on total RNA and DNA synthesis and on ribosomal and heterogenous RNA in L1210 cells. These drugs inhibit RNA synthesis preferentially over DNA and in both types in the order AD32 less than AD less than 4'-epi AD. All three compounds inhibited nuclear rRNA, non-poly (A) HnRNA, and poly (A) HnRNA. By measuring the inhibitory effect of adriamycin and its derivatives in the presence of low concentrations of Act D, it was established that approximately one-half of the inhibition applies to non-ribosomal RNA. There appears to be no qualitative effect on the processing of ribosomal RNA from larger precursor molecules, no effect upon the uptake of uridine, and the effect of the anthracylines on RNA synthesis appears to be at least partially reversible.